ECG is a topic which most of us doctors at our early phase of life face problem in reading and assessing.....so here is a simplest version which will help u.....

1. - DR.AKIF A.B
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5. P-waves
P-waves represent atrial depolarisation.
In sinus rhythm, there should be a P-wave preceding
each QRS complex.
PR interval
The PR-interval is from the start of the P-wave to the start of
the Q wave.
It represents the time taken for electrical activity to
move between the atria and ventricles.
QRS complex
The QRS-complex represents depolarisation of the ventricles.
It is seen as three closely related waves on the ECG (Q,R and S
wave).
STEP TO PG-MD/MS - DR.AKIF A.B

6. QT-interval
The QT-interval starts at the beginning of the QRS complex and
finishes at the end of the T-wave.
It represents the time taken for the ventricles to depolarise and
then repolarise.
T-wave
The T-wave represents ventricular repolarisation.
It is seen as a small wave after the QRS complex.
ST segment
The ST-segment starts at the end of the S-wave and finishes at
the start of the T-wave.
The ST segment is an isoelectric line that represents the time between
depolarization and repolarization of the ventricles (i.e. contraction).
STEP TO PG-MD/MS - DR.AKIF A.B

7. V1 – 4th intercostal space – right sternal edge
V2 – 4th intercostal space – left sternal edge
V3 – midway between V2 and V4
V4 – 5th intercostal space – midclavicular line
V5 – left anterior axillary line – same horizontal level as V4
V6 – left mid-axillary line – same horizontal level as V4 & V5
CHEST ELECTRODES POSITIONS
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9. V1 Septal view of heart
V2 Septal view of heart
V3 Anterior view of heart
V4 Anterior view of heart
V5 Lateral view of heart
V6 Lateral view of heart
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10. LIMB ELECTRODES
LA left arm
RA right arm
LL left leg
RL right leg – neutral – not used in
measurements
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11. OTHER LEADS
Lead I Lateral view (RA-LA)
Lead II Inferior view (RA-LL)
Lead III Inferior view (LA-LL)
aVR Lateral view (LA+LL – RA)
aVL Lateral view (RA+LL – LA)
aVF Inferior view (RA+LA – LL )
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13. -Each small square represents 0.04 seconds
-Each large square on the paper represents 0.2 seconds
-5 large squares therefore = 1 second
- 300 large squares = 1 minute
HOW TO READ ECG PAPER
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14. The shape of the ECG waveform
-When the electrical activity of the heart travels towards a lead you get
a positive deflection.
- When the electrical activity travels away from a lead you get a negative
deflection.
Electrical activity in the heart flows in many directions at once.
The wave seen represents the average direction.
The height of the deflection also represents the amount of electricity
flowing in that direction.
The lead with the most positive deflection is closest to the direction the
hearts electricity is flowing.
If the R-wave is greater than the S-wave it suggests depolarisation is
moving towards that lead.
If the S-wave is greater than the R-waves it suggests depolarisation is
moving away from that lead.
If the R and S-waves are of equal size it means depolarisation is travelling at
exactly 90° to that lead.
STEP TO PG-MD/MS - DR.AKIF A.B

15. In healthy individuals you
would expect the axis to
lie between -30° and +90º.
The overall direction of electrical
activity is towards leads
I,II and III (the yellow arrow
below).
As a result you see a positive
deflection in all these leads,
with lead II showing the most
positive deflection as it is
the most closely aligned to
the overall direction of
electrical spread.
STEP TO PG-MD/MS - DR.AKIF A.B

16. You would expect to see the most negative deflection in aVR. This is due
to aVR looking at the heart in the opposite direction to the overall electrical
activity.
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17. Right axis deviation
Right axis deviation (RAD) is usually caused by right ventricular
hypertrophy.
In right axis deviation the overall direction of electrical
activity is distorted to the right (between +90º and +180º).
Extra heart muscle causes a stronger
positive signal to be be picked up by leads
looking at the right side of the heart.
This causes the deflection in lead I to become
more negative and the deflection in III
to be more positive.
RAD is associated with pulmonary
conditions as they put strain on the right
side of the heart.
It can also be a normal finding in very
tall individuals
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18. deflection in lead I to become more negative and the
deflection in III to be more positive.
RIGHT AXIS DEVIATION
Normally : Lead II is more positive than Lead I & III
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19. In left axis deviation (LAD) the direction of overall electrical
activity becomes distorted to the left (between -30° and -90°).
This causes the deflection in lead I to become more positive and
the deflection in III to be more negative.
LAD is usually caused by conduction defects and not by increased
mass of the left ventricle.
LEFT AXIS DEVIATION
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20. Normal Cardiac axis Right axis deviation Left axis deviation
Lead II is more positive
than Lead I & III
Lead III is more positive
than Lead I & II
Lead I is more positive
and Lead II & III are
negative
Normal Cardiac axis
Right axis deviation
Left axis deviation
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21. The mnemonic RRAW can help you remember
what you should be looking for and in what
order:
Rate
Rhythm
Axis
Waveform (the various parts of the ECG mentioned
above)
Reading ECGs
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22. Heart rate can be calculated simply with the following method:
Work out the number of large squares in one R-R interval
Then divide 300 by this number and you have your answer
e.g. if there are 4 squares in an R-R interval 300/4 = 75 beats per minute
RATE
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23. Look at the R-R intervals again – if they are equally spaced from each other
the rhythm is regular. If not the rhythm is irregular.
You can use the ‘card method’ to mark out the distance between each R
wave to check the spacing.
An irregular rhythm with no distinct P-waves suggests atrial fibrillation.
RHYTHM
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24. Cardiac axis describes the overall direction of electrical spread
within the heart.
In a healthy individual the axis should spread from 11 o’clock to 5
o’clock.
To figure out the cardiac axis you need to look at leads I,II and III.
AXIS
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25. Normal cardiac axis
In normal cardiac axis Lead II has the most
positive deflection compared to Leads I and
III
Right axis deviation
In right axis deviation Lead III has the most
positive deflection and Lead I should be
negative.
This is commonly seen in individuals with
right ventricular hypertrophy.
Left axis deviation
In left axis deviation Lead I has the most
positive deflection and Leads II and III are
negative.
Left axis deviation can suggest underlying
heart conduction system defects.
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26. Normal duration = 120 msec
Represents Atrial
Depolarisation
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27. P-waves represent atrial depolarisation.
In sinus rhythm, there should be a P-wave preceding each QRS complex.
Look at the p waves and comment on a number of things:
•Are P-waves present?
•Do they occur regularly?
•Is there sinus rhythm (does a P-wave precede each QRS complex?)
•Do the P-waves look normal? (smooth, rounded and upright)
•If P-waves are absent and there is an irregular rhythm it may suggest atrial
fibrillation.
P-waves
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28. Seen in MITRAL STENOSIS
P-PULMONALE
Seen in Right Atrial
Hypertrophy
P-MITRALE
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29. The P-R interval should be between 0.12-0.2 seconds (3-5 small squares).
P-R INTERVAL
Normal duration =
120-200 msec
PR interval
The PR-interval is from the start of the P-wave to the start of
the Q wave.
It represents the time taken for electrical activity to
move between the atria and ventricles.
Short PR Interval
(<120msec)
Prolonged PR Interval
(>200msec)
Tachycardia Heart Blocks
Wolf Parkinson White Sx
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31. SA Node
AV Node
ECG :
PR interval is
Prolonged but remains
constant
Treatment :
Oral Atropine ( Pacemakers is of no use since defect is in conduction but not at nodes)
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32. Dropped
Beat
-Poor conduction of AV node
-PR interval lengthens i.e is not constant
-Sudden missed beats present
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34. -Poor conduction of Bundle of His
-PR interval= Normal and is constant
-Heart rate is low
-Treatment : Pacemakers
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35. -Complete destruction of AV node
-P-P Interval : Not constant
-R-R Interval : Mot constant
-Rx: Pacemaker
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36. Used In Not used in
Sick sinus Sx 1st Degree Heart Block
Mobitz type II Mobitz Type I
3rd Degree Heart Block
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37. Duration =80-120msec (2
small squares)
QRS complex
The QRS-complex represents depolarisation of
the ventricles.
It is seen as 3 closely related waves on the
ECG (Q / R / S wave):
•The first downward deflection is the Q-wave
•Any upward deflection is an R-wave
•A downward deflections after an R-wave is called
the S-wave
Check the width of the QRS complexes:
•The QRS complexes should be approximately 0.12
seconds (3 small squares)
If longer than 0.12 seconds it suggests the complex
originated in the ventricles.
If shorter than 0.12 seconds it suggests the
complex is supraventricular in origin.
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39. J Wave or Osborne wave
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41. 2) Atrial Fibrillation
3) PSVT
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42. -Paroxysmal Supraventricular Tachycardia
-Only Arrhythmia which can occur in Normal Heart
-Spontaneous termination with vomiting since it stimulates vagus
-R-R Interval is shortened but is constant
-Hidden P waves
Sudden onset of PSVT
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43. -Ectopic focus = At Cavo Tricuspid Isthmus
-Rate = 240-350
-AV Nodal block = 2:1
-Max. Heart rate : 175bpm
-R-R Interval : Shortened but constant
-Narrow complex QRS
-Flutter/ Saw tooth waves
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44. ATRIAL FLUTTER ATRIAL FIBRILLATION
Ectopic focus : Cavo Tricuspid Isthmus Left atrium
Atrial Rate : 240-350 300-600bpm
AV nodal block : 2:1 4:1
Max. Heart rate : 350/2 = 175bpm (AV
nodal block=2)
600/4 = 150bpm
R-R Interval : Decreased and constant Decreased and variable
Narrow complex QRS Narrow complex QRS
PSVT is differentiated from Atrial
flutter by presence of only one P wave
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45. -Ectopic site of firing is present on ventricle
-Ventricular rate = 200bpm
-Atria is under SA node control. Hence Atrial Rate =100bpm
-So Atrio Ventricular Dissociation
STEP TO PG-MD/MS - DR.AKIF A.B

46. CAUSES
Hypokalemia ( Cholera)
Hypomagnesemia (
Gitelman Sx)
Class IA/IC/III Anti-
arrhytmic drugs
Erythromycin +
Astemizole/Terfinadine/Ket
oconazole
Erythromycin + Cisapride
Treatment : Magnesium Sulphate
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47. -Na+ channel defect
-ST segment elevation + T wave inversion
+ve h/o sudden death of sibling
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49. -MC Arrhythmia of Digoxin Toxicity
-Most characteristic arrhythmia of Digoxin Toxicity = Non Paroxysmal Atrial
Tachycardia with AV block
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50. The ST-segment starts at the end of the S-wave and finishes at
the start of the T-wave.
It represents the interval between ventricular
depolarisation and repolarisation.
It should be level with the PR-segment and the T-P
segment in healthy individuals.
ST SEGMENT
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51. ST ELEVATION
ST elevation is significant when it is
greater than 1mm (1 small square) in 2 or more contiguous limb leads or
>2mm in 2 or more chest leads.
It is most commonly caused by acute full thickness M.I
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Normal ECG

53. Artery compromised Leads
Lateral wall M.I Left Circumflex
vessels
V5, V6 , I, aVL
Septal wall M.I Septal Br. Of Left
Anterior descending
A.
V1, V2, I,aVL
Anterior wall M.I LAD V1- V4 , I, aVL
Extensive AWMI LMCA V1- V6 , I, aVL
Post. Wall M.I Post. Descending
Artery > Lt.
Circumflex A.
V7, V8,V9 : ST
elevation
V1-V4 : ST
depression
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58. ST DEPRESSION
ST depression ≥ 0.5 mm in ≥ 2 contiguous leads indicates myocardial ischaemia.
ST depression
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ST SEGMENT Elevation
Other Features
1) Pericardial Friction Rub
2) MC Cause : TB

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Causes
1) Pericardial effusion
2) Restrictive cardiomyopathy
3) Myxoedema
4) Obesity

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ECG Changes in Atrial Fibrillation
1) Variable R-R Interval
2) Narrow QRS (normal QRS=80-
100msec : 2 small squares)
3) Absent P waves

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Na+ channel blockage Decreases slope of Phase 0
K+ channel blockage Increases duration of action
potential
K+ channel opener Decrease duration of action
potential

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--- a) Na+ channel blockage
--- b) K+ channel blockage
--- c) K+ channel opener
a)
b)
c)
Phase 0
Phase 2
Phase 1
Phase 3
Phase 4Phase 4

68. STEP TO PG-MD/MS - DR.AKIF A.B
Action potential difference = QT interval
K+ channel blockers
K+ channel
blockage
Increases
duration of
action potential
K+ channel
opener
Decrease
duration of
action potential

69. STEP TO PG-MD/MS - DR.AKIF A.B
Na+ channel = Depolarisation(QRS wave)
Na+ channel blockage = Increases QRS duration
K+ channel = Repolarisation(QT interval)
K+ channel Blockage = Prolongs QT interval
K+channel Opener = Shortens QT interval

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Class I Na+ channel blocker
Class II Beta blockers
Class III K+ channel blocker
Class IV Calcium channel blocker
Class V Others

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Ia Ib Ic
Na+ channel blockage Na+ channel blockage Na+ channel blockage
K+ Channel blockage K+ channel opener No effect on K+ channel
Quinidine
Procainamide
(S/E:SLE)
Lignocaine
Phenytoin
Tocainide
Encainide
Flecainide
Propafenone
Queen – Quinidine
Princess -
Procainamide
Used only for ventricular
Arrhythmias

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PROPRANOLOL
METOPROLOL
BETA BLOCKERS

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B – Bretylium
I – Ibutilide
N – No
D – Dofetilide
A – Amiodarone
S - Sotalol

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-Metabolised by microsomal enzymes
-Have all the 4 mechanisms : Na+ #
K+ #
Beta #
Ca #
-Longest acting (T1/2 = >3wks)
-Used for all Arrhytmias except Torsades De pointes ( Since it prolongs QT interval)
-

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The = Thyroid (Hypo or Hyper)
Periphery of = Peripheral Neuropathy
My = Myocardial Depression
Lung & = Lung fibrosis
Cornea is = Corneal deposits
Photosensitive = Photosensitivity

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Calcium Channel Blockers
-Verapamil
-Diltiazem
- Dipines do not act on heart.

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Digitalis DOC for Atrial fibrillation +
CHF
Atropine Used for Bradyarrhythmias
- DOC for AV block
Adenosine Shortest acting Anti-Arrhythmias
(T1/2 < 10sec)
- DOC for PSVT
MgSO4 DOC for Torsades De Pointes

80. STEP TO PG-MD/MS - DR.AKIF A.B
Atrial fibrillation and flutter -Acute attack = I.V Ibutilide
-Rhythm control = Amiodarone
-Rate control = Beta blockers
Anticoagulation in Atrial
Fibrillation
Noval Oral Anticoagulants
-Dabigatran
-Apixaban
PSVT Treatment = I.V Adenosine
Prophylaxis = Verapamil or Beta
Blockers
SVT Treatment and Prophylaxis =
Verapamil> Beta blockers
- Associated with CHF = Digoxin

81. STEP TO PG-MD/MS - DR.AKIF A.B
Torsades De Pointes Magnesium sulphate
Ventricular extrasystole Beta Blockers
Ventricular fibrillation Amiodarone
Digitoxin Toxicity Lidocaine
Ventricular Tachycardia in M.I Lidocaine
WPW Sx Procainamide

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